This invention relates generally to card clothing, and is concerned in particular with enhancing the efficiency of fibre transfer to doffers and workers during textile carding.
A critically important aspect of carding is the efficiency of transfer of fibre from the main cylinder, or swift, to the doffer. Low transfer efficiency leads to excessive recycling of fibre around the swift, which in turn decreases the quality of the product through increased fibre breakage and the incidence of nep in the web. In worsted processing, this increased fibre breakage results in a reduction of the average fibre length or hauteur in the combed wool product. Doffer wire is designed and manufactured specifically to maximise the transfer efficiency by ensuring that the working angles are optimised and that the points of the teeth are sharp. The lifetime of the wire is maximised by appropriate metallurgy and heat treatment of the wire during manufacture.
The workers on cards function in the same way as doffers and the technology described herein, so far as it relates to doffer wire, applies equally to worker wire.
Disclosures of metallic card clothing are to be found in U.S. Pat. Nos. 4,964,195, 5,581,848 and 5,755,012. U.S. Pat. No. 4,964,195 describes a card wire in which, in order to improve the carding action, the teeth are formed to have hooked tips to open up neps. This hooked tip has a flat top and a convex underside to the straight inside edge of the tooth, although the corresponding commercial product has an underside of the tooth that is flat or nearly flat and inclined to the wire base. The flat top is thought to act as a fibre deflecting surface and so reduce the total opening available to receive the fibres between the teeth. U.S. Pat. No. 5,581,848 describes a combing or carding tooth with a second tip in the combing front edge.
Another known wire for carding applications has longitudinal grooves cut on both sides of the teeth. This wire is called xe2x80x9cserratedxe2x80x9d wire, and its object is to improve the doffing of slippery fibres by providing a notch in the sides of the tooth that prevents the fibres slipping off the pins. Tests by the present applicant have shown that it is of quite limited value for this purpose, even where the grooves are of rectangular cross-section and relatively deep.
FIG. 1 illustrates the successive stages in the transfer of a longer fibre 8 from a swift 4, indicated at the left, to a doffer 6. Successive positions of the fibre 8 are depicted at a to g. The arrows 4a, 6a, show the directions of rotation. Once a fibre loops around a doffer tooth 7, it is subsequently straightened (position a) and held under tension by the teeth 5 of the swift 4 because of the much higher surface speed of the swift and the forward angle of the teeth. Given that the fibre on the doffer is under tension, the position evolves to one in which the fibre is normal to the surface of the doffer, provided the doffer tooth can hold the fibre. The actual angle achieved depends on the magnitude of the coefficient of friction between the fibre and the respective metal wires.
Previous analyses of doffer wire efficiency have emphasised the effectiveness of fibre pick-up and have ignored the effect of fibre loss from the pins, which will ultimately determine the level of transfer efficiency. For a doffer operating at equilibrium running conditions, the smaller the transfer efficiency to the doffer, the thicker the layer of recycled fibre on the swift, and the smaller the grip of the teeth of the swift on the fibre held by the doffer. In turn, this reduces the tension in the fibre and increases the chance that the fibre will be retained by the doffer. In effect, doffers rely on recycled fibre to reduce the grip of the pins of the swift so that transfer from the swift can occur. Thus, doffer efficiency is a dynamic function of the design of the doffer wire and the nature of the fibre being processed.
An object of this invention, at least in one application, is to increase the efficiency with which fibres are transferred from the swift to the doffer. The invention also has application to the design of worker wire because workers operate in exactly the same way as doffers.
The invention essentially entails the concept that enhanced fiber transfer efficiency can be achieve by forming one or more undercuts on the forward or inside face of the overhanging teeth or carding wire on the take-up component in a card transfer stage. The one or more undercut preferably includes a portion substantially parallel to the longitudinal direction of the wire, ie the peripheral surface of the cylindrical structure on which the wire is wrapped.
The invention accordingly provides card clothing comprising a strip of profile wire having a plurality of longitudinally aligned teeth with respective overhanging tips, wherein the edge-face of each tooth under the overhanging tip includes at least one undercut edge-segment spaced along the edge-face from the tip, which undercut edge-segment increases the retention of fibres by said edge-face during carding.
Preferably, there are a plurality of said edge-segments spaced apart and from said tip along said edge-face.
Advantageously, there are multiple undercut edge-segment in said edge-face and the spacing of these edge-segments increases in a direction away from the tip of the tooth.
In an embodiment, each of the edge segments has an extremity in the longitudinal direction of the profile wire, and these extremities of the edge segments and the tip are in alignment.
In one arrangement, the edge-face includes a tip portion adjacent said tip, a base portion adjacent said base, and one or more backset portions between the undercut edge-segment, and wherein said one or more basket portions, said tip portion and said base portion are generally parallel.
In another embodiment the one or more undercut edge-segment is provided by a notch or scallop recess in said edge-face.
The invention also provides a card roll, eg. a doffer or worker, clothed with card clothing according to the invention, and to a card including one or more such rolls.